Naltrexone

Published 8 December 2011.

Naltrexone (e.g. Naltrexon Vitaflo 50 mg) has been used in the management of alcohol dependence since the late 1990s. It is an opioid receptor antagonist. The opioid system modulates dopamine release in the body. As an opiate inhibitor, naltrexone reduces the enjoyment of alcohol. It is designed to increase the number of sober days and reduce relapses as well as the risk of uncontrollable consumption following a small amount. It also has the effect of reducing the total volume of alcohol consumed. Patients using naltrexone are able to continue drinking and concomitant use with alcohol does not pose a serious health risk.

The evidence for the efficacy of naltrexone in the treatment of alcohol dependency is not completely conclusive as in some studies the placebo has been shown to be as effective as the treatment itself. In general, however, the evidence supports the use of naltrexone. Naltrexone is also indicated in the treatment of a number of other conditions although they are not discussed in this article. Naltrexone should not be confused with naloxone, which is used to reverse the effects of opioid usage.

Dosage

Naltrexone treatment can be commenced even if the patient remains under the influence of alcohol. The recommended dose for adults is 50mg daily, preferably in the morning. The recommendation is for the initial treatment phase to be carried out over three months. There are no restrictions on the total duration of the treatment. Naltrexone can also be used on an “as required” basis, i.e. during high-risk situations such as parties, holidays and strong cravings for alcohol.

Naltrexone treatment should be initiated by a specialist and the treatment should be monitored. During treatment, psychosocial support is provided to help the patient discontinue alcohol use. This is why the initial treatment phase must be sufficiently long. In order to reduce the risk of side effects, the initial dose can be kept very low and increased gradually. Long-term naltrexone treatment can be discontinued quickly as it is not addictive. However, some patients may benefit from a gradual withdrawal.

Naltrexone is not recommended for under-18s and elderly patients, as there is not sufficient evidence available on the effects of use on these populations. Similarly, it is not recommended for pregnant and breastfeeding women due to lack of evidence.

Naltrexone is a prescription-only medicine. It is available at pharmacies but patients are only eligible for Kela reimbursement on the basis of a so-called Medical Statement B (B-lausunto), which can be issued by a doctor. The statement, which sets out the clinical indications for treatment, should be forwarded to Kansaneläkelaitos (Kela, the Social Insurance Institution of Finland). Kela will assess your eligibility for reimbursement. The reimbursement is subject to psychosocial interventional being provided alongside the drug treatment. The reimbursement status is valid for three months at a time.

Characteristics of naltrexone

Naltrexone is suitable for long-term use. A Finnish study found that naltrexone reduced the number of drinking days and the number of drinks consumed. Relapses were also reduced. Key to successful outcomes was the psychosocial support provided alongside the treatment. Naltroxone is especially effective for therapeutic regimens that do not require total abstinence.

Naltrexone is absorbed rapidly, with peak concentration achieved in approximately an hour. Naltrexone is converted to active metabolites in the body, which reduces the total period of effectiveness. As a result, naltrexone can be taken once daily. Naltrexone does not cause mental or physical addiction or tolerance.

Side effects and interactions

Extremely common side effects of naltrexone treatment include nausea, agitation and listlessness. Common side effects include GI complaints (diarrhoea, constipation), low mood, dizziness and erectile dysfunction. It is worth noting that not all of these side effects are due to naltrexone itself but may rather be associated with the reduction and cessation of possibly prolonged alcohol use (hangover, poor general health). Naltrexone may impair the ability to drive and operate machinery. Liver function should be tested prior to commencing treatment and monitored throughout.

Naltrexone is contraindicted with opioid analgesics, including fentanyl and morphine, and opiate replacement therapy (buprenorphine, methadone). Naltrexone may block the opioid effects and even cause severe withdrawal symptoms. The withdrawal symptoms should not be treated with an increase dose of the opiate as once the effects of naltrexone wear off, it may lead to respiratory depression and death.

To date, no high-quality interaction studies have been performed and, as such, no data on naltrexone-drug interactions are available. It is know that naltrexone increases acamprosate concentrations. Acamprosate, also used in the treatment of alcohol dependence, is not licensed for use in Finland but is available through a so-called special permit for compassionate use. Naltrexone can be combined with disulfiram, which prevents the consumption of alcohol entirely, but due to their hepatic effects, the period of concomitant use should be kept brief.

Overdose

Naltrexone is a reasonably safe medicine. In studies, even large doses (up to 800mg daily for seven days) have not led to serious side effects. If you suspect a naltrexone overdose, it is a good idea to contact a doctor immediately, including out-of-hours if necessary. Treatment is symptomatic.